This invention relates to a pressure differential and pulsation dampener control device for an expansible sleeve-type gas flow control valve.
In natural gas well production, for example, expansible sleeve-type flow control valves are commonly used to control production flow from a compressor to a delivery pipe line, with production from a well being measured on a daily basis to provide a record of the production level. However, gas compressors have an inherent pulsation problem which may cause inaccuracies in the devices used to measure production. Attempts have been made to alleviate this problem by using expansible sleeve-type flow control valves to create back pressure on the compressor and reduce pulsation so that an accurate production measurement can be made.
A typical sleeve-type flow control valve may, for example, comprise a body having inlet and outlet passages between which is positioned a circular barrier member with a space around it within the housing providing a flow path through the housing around the barrier member. A cylindrical sleeve of resilient material fits snugly over the barrier member and is sealed at its opposite ends within the housing. The internal diameter of the sleeve is normally slightly smaller than that of the barrier member so that it is stretched over the barrier member to provide a snug sealing fit under the force of the tensioned resilient material in the absence of fluid pressure acting against it. The barrier member prevents fluid flow directly through the valve and normally the sleeve prevents flow around the barrier member. However, at sufficient inlet pressure, the fluid expands the sleeve outwardly and flows between the barrier and the sleeve to the outlet flow passage.
In normal operation, a control pressure is introduced into the housing around the resilient sleeve to oppose its outward expansion and maintain the sleeve in sealed relationship as long as the control pressure is as great or greater than the upstream pressure. Then, in the event that the control pressure, in conjunction with the tension of the expansible sleeve is overcome, the sleeve expands outwardly to permit flow through the valve body. It is in the control of the pressure around the expansible sleeve where attempts have been made to maintain a consistent back pressure and reduce pulsation without adversely affecting production.
The invention provides a control device which maintains a substantially constant upstream and downstream pressure differential across a sleeve-type flow control valve while at the same time minimizing pulsations.